Even when your result was not good, sharing is always an option. I learned alot about LUA and Renoise API in recent days, because of several questions from @Raul and others in the API forum. Also the Paddles tool got me on point, how to achieve grids. My approach of a piano roll: 
Its not ready to use. I’ll post it here and on github, when it’s kind of usable. So everyone can see the code and maybe we can improve it even more. Renoise API and the view builder is pretty limiting, but for some basic piano roll it’s enough.
Edit: Made a twitter post to show the current state in action: https://twitter.com/xoonx/status/1350788024465055744
Edit 2: Forum post about this tool: Another piano roll: com.dufte.SimplePianoroll.xrnx